CAMPTOTHECIN-BINDING SITE IN HUMAN SERUM-ALBUMIN AND PROTEIN TRANSFORMATIONS INDUCED BY DRUG-BINDING

Circular dichroism (CD) and Raman spectroscopy were employed in order to locate a camptothecin (CPT)-binding site within human serum albumin (HSA) and to identify protein structural transformations induced by C PT binding. A competitive binding of CPT and 3'-azido-3'-deoxythymidin e (a ligand occupying IIIA structural sub-domain of the protein) to HS A does not show any competition and demonstrates that the ligands are located in the different binding sites, whereas a HSA-bound CPT may be replaced by warfarin, occupying IIA structural sub-domain of the prot ein, Raman and CD spectra of HSA and HSA/CPT complexes show that the C PT-binding does not induce changes of the global protein secondary str ucture, On the other hand, Raman spectra reveal pronounced CPT-induced local structural modifications of the HSA molecule, involving changes in configuration of the two disulfide bonds and transfer of a single Trp-residue to hydrophilic environment, These data suggest that CPT is bound in the region of inter-omain connections within the IIA structu ral domain of HSA and it induces relative movement of the protein stru ctural domains. (C) 1997 Federation of European Biochemical Societies.